Testing optimality for quadratic 0–1 unconstrained problems

This paper analyses a necessary and sufficient optimality condition for quadratic pseudo-Boolean unconstrained problems. It is proved that in general testing any necessary and sufficient optimality condition is a difficult task for anyNP-hard problem. An-optimality condition is derived together with an approximation scheme to test it.This work has been supported by the Progetto Finalizzato Trasporti 2, 93.01799.PF74.Professor Paolo Carraresi died unexpectedly on March 5, 1994. At the time of his death this paper had been completed. While undertaking the final revision, the other two authors were reminded just how much they were indebted to Professor Carraresi after many years of common work together.     

Effects of the nanofiller size and aspect ratio on the thermal and rheological behavior of PEG nanocomposites containing boehmites or hydrotalcites

Journal of Thermal Analysis and Calorimetry - In this work, polyethylene glycol nanocomposites containing different nanofillers (namely hydrotalcites or boehmites, at 5 mass% loading) were...     

Intercalation effects in LDPE/o-montmorillonites nanocomposites

Typical montmorillonite clays (Cloisite^® Na⁺, Cloisite^® 30B) were modified by treatment with octadecyl ammonium chloride (ODC) and successive additions of octadecylamine (ODA). XRD analyses of the modified clays indicated an increase of the basal spacing of the (0 0 1) planes depending on the ODC or ODA additions.Nanocomposites were prepared by dispersing the modified clays (3% w/w concentration) in LDPE, using a Brabender mixer. XRD measurements of the obtained products indicated in some cases the achievement of intercalation effects, which were confirmed by TEM analysis.Some thermal, mechanical, dynamic-mechanical and rheological properties were evaluated and correlated to the degree of intercalation.     

Hyperbolic set covering problems with competing ground-set elements

Motivated by a challenging problem arising in wireless network design, we investigate a new nonlinear variant of the set covering problem with hyperbolic objective function. Each ground-set element (user) competes with all its neighbors (interfering users) for a shared resource (the network access time), and the goal is to maximize the sum of the resource share assigned to each ground-set element (the network efficiency) while covering all of them. The hyperbolic objective function privileges covers with limited overlaps among selected subsets. In a sense, this variant lies in between the set partitioning problem, where overlaps are forbidden, and the standard set covering problem, where overlaps are not an issue at all. We study the complexity and approximability of generic and Euclidean versions of the problem, present an efficient Lagrangean relaxation approach to tackle medium-to-large-scale instances, and compare the computational results with those obtained by linearizations.     

Thermal stability and flame retardancy of polyester fabrics sol–gel treated in the presence of boehmite nanoparticles

Polyester fabrics have been treated with hybrid organic-inorganic sols containing aluminium hydroxide, namely a synthetic boehmite. The treated fabrics have been thoroughly investigated by infrared spectroscopy, scanning electron microscopy coupled to elemental analysis and thermogravimetry. Furthermore, the flammability of the coated fabrics has been assessed and compared with that achieved by applying the two components separately. More specifically, flammability tests have shown that the sol–gel treatment in the presence of boehmite nanoparticles is able to suppress the dripping phenomenon, which represents the main issue to fulfil for polyester fabrics.     

Properties of networks based on poly(alkylene glycol) diacrylates

Three series of poly(alkylene glycol) diacrylates, namely poly(ethylene glycol), poly(propylene glycol) and poly(tetramethylene glycol) α,ω-diacrylates have been prepared by acryloylation of the corresponding bis-OH-terminated oligomers. Their MW was in the range 200–1000 and their acrylic functionality was close to two. They were subjected to UV curing as thin films obtaining, by FTIR analysis, complete terminal double bond conversion in all cases with the exception of the lowest MW oligomers. Thermal and mechanical properties of the networks were investigated by means of DSC, TMA and DMTA analyses. Concerning the PPGDA oligomers, products totally amorphous and rubbery were obtained; PEGDA and PTMGDA oligomers gave similar amorphous structures with the exception of the highest MWs which showed partial crystallinity. By means of thermal and DMTA measurements, T_g values and E' moduli were obtained and correlated to the MW of the oligomers used. In particular, T_g values, as function of the crosslinking density, agreed with those calculated by the Nielsen equation for the three series investigated. The equilibrium swelling in water was determined for various networks as a function of the MW of the oligomers. The values obtained were compared and discussed in terms of the solubility parameters and the crosslinking density of various structures.     

The role of pre-hydrolysis on multi step sol–gel processes for enhancing the flame retardancy of cotton

The flame retardancy properties of cotton have been enhanced by exploiting an optimized multistep sol–gel process, consisting of a pre-hydrolysis step, followed by consecutive depositions of hybrid phosphorus-doped silica layers, using DPTS as precursor of the oxidic phases. Upon optimization, it has been demonstrated that just one phosphorus-doped silica layer is able to strongly reduce the heat release rate (?52 %), and the total smoke release (?56 %) and its rate (?62 %) with respect to the untreated fabric. In addition, the deposition of three layers allows achieving a higher flammability resistance if compared to a single layer, as indicated by the final residue after the flammability tests. As far as flammability resistance is concerned, the new coatings have shown a good durability when subjected up to five washing cycles according to ISO 6330 standard.